EXPLORING LINKAGES BETWEEN SUBCRITICAL CRACK GROWTH AND ROCK TYPE DEPENDENT EROSION RESISTANCE, A CASE STUDY FROM THE BLUE RIDGE, VA
Weathering-related stresses that typically arise in surface or near surface bedrock are relatively low and unlikely to exceed the tensile strength of most rock types. Thus mechanical weathering in these rocks likely occurs most commonly through subcritical crack growth, an idea that has been largely overlooked (Eppes et al., 2016). Here, we explored this hypothesis by comparing and contrasting known fracture mechanics properties for the Shenandoah study rock types: sandstone, quartzite and granitoids. From the exact outcrops for which 10Be samples were collected, we also gathered in-situ crack data (size, density, degree of rounding of crack edges, spall thickness), as well as samples for SEM analysis, thermal conductivity and uniaxial compression tests. Preliminary results support causal relationships between rock properties that influence subcritical crack growth and cracking patterns. For example, observed high crack density in slowly eroding quartzite outcrops is consistent with measures of a low subcritical crack growth index but high fracture toughness for that rock type and with the complex microstructure of the skolithos-bearing Antietam quartzite of Shenandoah. Ultimately we believe that conceptualizing erosion resistance in terms of subcritical crack growth could provide a unifying mechanistic paradigm for other previously observed relationships between erosion and rock properties like joint spacing, quartz content and compressive strength.